1. Field of the invention
The present invention relates to a method for cleaning the inside of a pipe in a semiconductor device fabricating machine, and more specifically to a method for removing an organic matter adhered on an inner wall surface of a gas piping parts such as a pipe and a joint in a semiconductor device fabricating machine.
2. Description of related art
In a DRAM (dynamic random access memory) which is one kind of semiconductor devices, the area of a memory cell has a tendency to reduce more and more in order to meet with a demand for an elevated integration density. If the area of the memory cell reduces, the amount of charge stored in the memory cell reduces correspondingly. As a result, it is becoming difficult not only to realize the elevated integration density but also to ensure a required amount of charge stored in the memory cell. Under this circumstance, in order to ensure a required amount of charge in the memory cell having a reduced cell area, it has been proposed to grow hemispherical grains on a surface of a capacitor electrode of a stacked capacitor by a HSG (hemi-spherical grain) technology so as to cause the capacitor electrode to have an increased effective surface area.
In a processing for growing the hemi-spherical grains in the HSG technology, there occurred a situation that the hemi-spherical grains abnormally grew with the result that an expected increased surface area of the capacitor electrode could not be realized. The inventor studied the cause of this problem, and found out that the cause is an abnormal growth of organic matters in an atmosphere before the hemi-spherical grains is grown or in the growing process of the hemi-spherical grains. The organic matters in an atmosphere result from the peeling-off of the organic matters adhered to an inner wall of a pipe, particularly, the peeling-off of organic matters adhered to an inner wall of a piping parts such as a pipe and a joint from a packing vinyl envelope. In other words, it has become severely required to have a high degree of purity concerning the organic matters in the piping parts. In the following, the term "pipe" will be used to include a piping parts other than the pipe, for example, a joint.
In the prior art, the inside of the pipe was cleaned up by using a relatively inexpensive high-purity N.sub.2 as a cleaning gas. However, occurrence of the above mentioned problem means that this prior art method for cleaning the inside of the pipe is no longer satisfactory.
One example of the method for cleaning up the inside of the pipe by use of N.sub.2, is disclosed in Japanese Patent Application Pre-examination Publication No. JP-A-04-145991 (an English abstract of JP-A-04-145991 is available and the content of the English abstract is incorporated by reference in its entirety into this application). In this prior art method, the inside of the pipe is cleaned up by alternately repeating a supplying of a liquid nitrogen into the pipe and a gas purging for the pipe.
The liquid nitrogen supplied from one end of the pipe into the inside of the pipe absorbs heat from the pipe or the outside of the pipe so that the liquid nitrogen is vaporized and therefore becomes a nitrogen gas. In this process, because of a cooling effect by the temperature of the liquid nitrogen itself having a boiling temperature of -197.degree. C. and because of a boiling of the liquid nitrogen, contaminant adhered to the inside of the pipe is peeled off and removed away. In the case of an organic micro-contaminant, the cooling effect causes the organic contaminant to contract so that an adhering force of the organic contaminant drops because of a difference in thermal expansion coefficient between the organic contaminant and a material of the pipe. On the other hand, the boiling of the liquid nitrogen peels off the organic contaminant adhered to the inside of the pipe by its physical action.
However, this prior art method for cleaning up the inside of the pipe, was insufficient in removing the organic matters, as mentioned hereinbefore. In addition, the boiling of the liquid nitrogen within the pipe is dangerous because a high pressure suddenly acts within the pipe.
Japanese Patent Application Pre-examination Publication No. JP-A-05-144802 (an English abstract of JP-A05-144802 is available and the content of the English abstract is incorporated by reference in its entirety into this application) points out that, in a method for cleaning up a heattreating pipe of an oxidation oven by baking the heat-treating pipe while supplying an inert gas such as N.sub.2 into the heat-treating pipe, there is a problem of an insufficient cleaning in that particles such as Na, Fe and Cu remain on an inner wall surface of the heat-treating pipe. In order to overcome this problem, JP-A05-144802 discloses a cleaning method of baking the heat-treating pipe by using a clearing gas which is the same as a processing gas.
In this prior art method, accordingly, when the semiconductor device fabricating machine having the heat-treating pipe is the oxidation oven, if an O.sub.2 gas is used as the process gas, the O.sub.2 gas is used as a cleaning gas. At this case, if a mixed gas composed of an O.sub.2 gas and an Ar gas is used in place of the O.sub.2 gas as the process gas, the mixed gas of the O.sub.2 gas and the Ar gas is used as the cleaning gas. Of course, in this oxidation treatment, the percentage of the O.sub.2 gas is high in the mixed gas of the O.sub.2 gas and the Ar gas. When the semiconductor device fabricating machine having the heat-treating pipe is a CVD (chemical vapor deposition) chamber, if a silane gas is used as the process gas, the silane gas is used as the cleaning gas. When the semiconductor device fabricating machine having the heat-treating pipe is an annealing oven, if an N.sub.2 gas is used as the process gas, the N.sub.2 gas is used as the cleaning gas.
The reason for using the cleaning gas which is the same as the process gas when the heat-treating pipe is baked, is that, whatever cleaning gas is used, only the contaminating particles of the limited kinds corresponding to the kind of the cleaning gas can be removed. Namely, all kinds of contaminating particles cannot be removed. Accordingly, if the cleaning is carried out by using the same gas as the process gas, it is possible to remove only the contaminating particles that can be removed by the cleaning gas. However, since the process gas which is the same as the cleaning gas is used in a succeeding process, no contaminating particles that can be removed by the process gas exists in the heat-treating pipe, so that no contaminating particles is conveyed to the semiconductor device fabricating machine by the process gas, and therefore, the processing can be carried out in a cleaned condition.
As mentioned above, this prior art method cannot completely remove all the kinds of inorganic contaminating particles such as Na, Fe and Cu, but is intended to remove only the removable contaminating particles since the semiconductor device fabricating machine is not contaminated by the contaminating particles that cannot be removed. In other words, this prior art method is not intended to remove organic contaminating particles, nor can it remove the organic contaminating particles.
Thus, in the prior art, there is no practical method for cleaning up the inside of the pipe, which can remove the organic matters adhered to the inside of the pipe in order to clean up the inside of the pipe to a high degree of cleanness so that the hemispherical grains can be grown by the HSG technology with causing no abnormal growth.